1. Field
The present invention relates generally to wireless communication, and more specifically to an improved method and apparatus for space-time pre-correction of transmitted wireless signals.
2. Background
Wireless communication carriers desire more wireless capacity. In other words, carriers desire to be able to service a greater number of subscribers within the same frequency band. To satisfy this need, code-division multiple-access (CDMA) systems have been proposed which are optimized for maximal wireless capacity. CDMA systems are often desirable over frequency-division multiple access (FDMA) or time-division multiple access (TDMA) systems for their robust performance in multipath environments. Multipath is a condition that occurs when a transmitter transmits a single signal that is received through multiple signal paths having different lengths. The difference in the lengths of the paths can cause different copies of the signals to interfere with each other. One standard for CDMA wireless communication called cdma2000 has been proposed by members of the 3rd Generation Partnership Project 2 (3GPP2). A system built to adhere to cdma2000 may operate in a mode that provides optimal capacity for voice users or in another mode that provides optimal capacity for packet data users.
One proposed approach to mitigating self-interference induced by multipath signals and frequency selective channels is space-time (S-T) equalization. S-T equalization can be used in a CDMA system, but requires complex signal processing methods and receiver hardware. Also, S-T equalization requires that each subscriber station include multiple receive antennas. The market for subscriber stations is very price-competitive, leading to a large desire of manufacturers to minimize the hardware cost of subscriber stations. The inclusion of additional antennas to the design of a subscriber station can substantially increase the cost of making the subscriber station. There is therefore a need in the art for ways to combat multipath interference without requiring subscriber stations to have multiple receive antennas.